1. Technical Field
The present invention relates to multilayer volume ray casting.
2. Discussion of the Related Art
Multilayer volume ray casting is an advanced technique built on top of standard volumetric ray casting that supports various efficient enhancements to standard volume visualization, such as cut-planes, crop-box, empty-space-skipping, punching masks, volume-of-interest masks, embedded multiplanar reconstructions (MPRs), and embedded curve and ribbon MPRs. The basic idea is to treat all the above descriptions as one or more volume-of-interest (VOI) definitions and use hardware accelerated surface rendering to convert the boundary models of these VOIs into a ray-layer buffer. The VOIs can have different priorities and multiple VOIs may overlap in three-dimensional (3D) space. The creation of the ray-layer buffer resolves the overlap according to the priorities. Each pixel of the ray-layer buffer then contains the information of a set of ray segments, including the starting locations and the material IDs. The multi-layer ray caster then renders each ray segment with the proper visualization parameters depending on the material ID.
A description of a VOI typically involves two parts: 1) a mask defining which voxels belong to the VOI, and 2) a set of viewing parameters that usually distinguishes the regions inside the VOI away from the region outside it. FIG. 1 shows a visualization example of a VOI inside a head dataset. The voxels enclosed in the VOI are rendered using a different color lookup table.
A mask can be specified as a binary volume since each voxel of the binary volume determines whether the voxel belongs to the VOI, or a closed polygonal mesh that defines the boundary between voxels inside the mask and voxels outside the mask. A mask in the form of a polygonal mesh may hereinafter be referred to as a geometric mask. Multilayer volume ray casting is particularly efficient in visualizing geometric masks.